At the time of battle in 1815, Waterloo was in what country?

The Battle of Waterloo was fought on Sunday, 18 June 1815, near Waterloo in present-day Belgium, then part of the United Kingdom of the Netherlands. A French army under the command of Napoleon Bonaparte was defeated by two of the armies of the Seventh Coalition: an Anglo-led Allied army under the command of the Duke of Wellington, and a Prussian army under the command of Gebhard Leberecht von Blücher, Prince of Wahlstatt.

Waterloo was the decisive engagement of the Waterloo Campaign and Napoleon's last. According to Wellington, the battle was "the nearest-run thing you ever saw in your life". Napoleon abdicated four days later, and on 7 July coalition forces entered Paris. The defeat at Waterloo ended Napoleon's rule as Emperor of the French, and marked the end of his Hundred Days return from exile. This ended the First French Empire, and set a chronological milestone between serial European wars and decades of relative peace.

The battlefield is located in the municipalities of Braine-l'Alleud and Lasne, about 15 kilometres (9.3 mi) south of Brussels, and about 2 kilometres (1.2 mi) from the town of Waterloo. The site of the battlefield today is dominated by a large monument, the Lion's Mound. As this mound was constructed from earth taken from the battlefield itself, the contemporary topography of the battlefield near the mound has not been preserved.